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Water Balance

      Swimming pool water balance is based on controlling a group of chemical physical parameters to protect the pool and the people in it.  The most important group is temperature, pH, total alkalinity, total dissolved solids (TDS), and calcium hardness.  These five relate to each other in a formula called the Langlier Saturation Index.  The saturation index was originally developed to help municipal water systems to predict the aggressiveness of drinking water, and to find the cheapest method to fix the problem.  If one factor in the index is high, and another is low, we don’t necessarily have to fix them – they will tend to cancel each other.  On the other hand, if all four factors are on the low side of normal, the water could still be dangerously aggressive.  Balancing these factors properly can be done with a chart and a calculator, but a computer does it much better. 

     In a swimming pool, we often look at several other factors that affect water without being directly part of the index.  Those factors are:  cyanuric acid, various metals (iron, copper, manganese); acid demand, base demand, phosphates, and a few others. 

Why Bother? 

     When the saturation index is too low, water is aggressively corrosive.  Aluminum, copper and stainless steel (like your filter heater and ladders) can rot out in a few years – instead of lasting 10-20 years.  Vinyl liners can weaken and develop a wrinkled, puckered finish called alligatoring.  Plaster can become etched so badly that people cut their feet walking in the pool – and that’s a couple of thousand dollars to fix! 

    In 1984, American swimmers preparing for the Los Angeles Olympics lost enamel from their teeth by swimming 12 hours a day in corrosive water.  Of course, they were spending more time in the water than most people, but some sensitive people will experience eye and skin irritation in unbalanced water. 

     When the index is too high, the water is scaling.  Pipes, hoses, fittings, and small areas of the filter can develop a hard precipitate (like cholesterol, in your arteries).  Water flow becomes reduced, and you have to run the filter longer to keep the pool clean.  A rough white scale may form on plaster walls, that can only be removed with a thousand dollar acid bath.  Unusually hard water may prevent pool chemicals, especially chlorine, from dissolving properly. 

     Pool chemicals were developed with the assumption that the consumer was putting them into properly balanced water.  Some will work perfectly well in any water, but some will work much better when you take care of the water. 

     Water balance is not expensive and is sort of permanent.  If you balance water and never change it, you never have to re-balance.  In a pool, however, you do add unbalanced water on a regular basis from rain, and refilling because of draining, back washing, winterizing, etc.  To make up for that, we recommend checking it out (we test it for free) three times a summer. 

     In any case, you really can’t escape the cost.  You either spend a little every year, or a lot every few years, fixing things that didn’t need to break. 

Langlier Saturation Index 

     Technically, the formula is:  pH + Ft, + Fta + Fca – Ftds = LSI.  Perfectly balanced water would give us an answer of 0.  Acceptably balanced water would range between -0.3 to +0.3.  If you really want to see how it works, we have a chart and some samples in our water lab.  We’ll be happy to show you.  The individual factors that we want to control are below. 

1.   pH is the most important.  Technically, the pH of water is not a chemical – it’s the exponent of the number of (0H)-ions in 1014 molecules of water.  More specifically, it’s the logarithm of the reciprocal of the molar concentration of the H+ ion.  Who thinks up these things?  Anyhow, think of it this way.  A pH of 7.0 is perfectly neutral.  6.0 is ten times as acidic.  5.0 is 100 times as acidic, 8.0 is ten times as basic or alkaline, and 9.0 is 100 times as basic.  In a swimming pool, chlorine is most effective at 6.5, and stops working all together at 8.0.  However, since your eyes have a pH around 7.4, we normally keep chlorine pools between 7.2 and 7.6.  Bromine pools are not as pH dependent, and are generally OK at 7.0 to 7.8.  Baquacil and Softswim pools have no dependence on pH, except eye comfort and water balance.  They are normally kept at 7.0 to 8.0. 

2.  Temperature can be kept anywhere, but we try to balance for the temperature that the water will be most of the time.  This is why your most important balance is right before you close.  We then input the average temperature over the winter – about 35°F.  That’s because an index that was low but terrible at 85°F, can become damaging at 35°F. 

3.  Total Alkalinity is the buffering capacity of the water.  Think of it as a shock absorber for the pH.  When the T.A. is low, your pool’s pH will be subject to large shifts up and down as rain, body oils, leaves, bird droppings, fill water, and other pool chemicals enter the water.  People with low T.A. are constantly fiddling with pH chemicals.  When the T.A. is normal (about 80-120 ppm), the pool’s pH tends to remain where it belongs.  High T.A. tends to lock the pH into place – which is fine if the pH happens to be ok, and rather annoying if you’re trying to move it on purpose. 

4.  Total Dissolved Solids is a measure of molecules that are dissolved in the water, but are not a part of the water.  There is a limit as to how much of this kind of molecule that the water can hold.  As the amounts rise, the water becomes cloudy, and the molecules may eventually precipitate out.  In some parts of the country, naturally occurring water starts out with a high TDS, as will some well water around here.  Certain chlorines, (Calcium hypochlorite, salt-to-chlorine generation, and sodium hypochlorite), will build up the TDS levels until the water becomes so cloudy that the pool has to be drained.  Common readings around here are 200 to 600 ppm, and problems aren’t expected until around 2500 ppm. 

5.  Calcium Hardness is the end point of the index.  Low calcium, (soft water) tends to bubble and foam like a bubble bath (soap and some algaecides are chemical softeners).  Just as low calcium in your blood will pull calcium out of your bones and teeth (like osteoporosis), low calcium in the pool will pull calcium, metals, minerals, and plasticizers from the pool, liner, heater, filter and ladders, and your eyes and teeth. 

     The proper level of calcium is roughly 200-250 ppm, but the actual amount depends on the pool finish and chemical system.  Plaster, concrete and gunite are mostly calcium and silica, so pools with those finishes must keep calcium levels within a very narrow range.  Black and colored plaster is even trickier.  Pools on calcium hypochlorite chlorine are kept low, because the chlorine adds calcium.  Pools on biguanide chemicals (Baquacil and Softswim) are kept high, because their biguanides and quaternary algaecides tend to soften water. 

Other Factors 

     While a water sample is being balanced, we will generally examine several related factors: 

1.  Metals:  Iron, copper and manganese, are not much of a problem inNew Hampshire surface water, but they can be a problem from well water. Metals cause pretty much permanent stains in the pool and fittings, especially when the pool is shocked.  The high oxidizer level of shock changes the metal ion from a colorless state to a colored state.  Iron becomes rust, which looks green spread out in the water, and rusty when it’s concentrated.  Copper becomes blue, and manganese black. 

     Our tests only read metals in the colorless state – they were designed to solve problems before they happen.  Once the metals have oxidized, we can’t read them.  To prevent staining, any level of iron or manganese is a problem (though manganese is very rare except for a couple of wells in Hollis and Townsend).  On the other hand, we see very high copper levels from people using copper algaecides and heaters being destroyed by unbalanced water – and we rarely hear complaints of copper staining.  

     High metal content does eat up sanitizers and shocks, though.  If you use a cheap sanitizer like chlorine, it may not be worth the expense of treating the metals.  If you use bromine, Baquacil or Softswim, it probably would save you money to treat it.  Bottom line:  before you spend money on mineral or metal control chemicals, talk to us. 

2.  Stabilizer, or Cyanuric Acid is important only in certain chlorine-based pools.  At the right level (30-40 ppm), stabilizer saves you money on chlorine, and keeps the chlorine active on sunny days.  Pools with salt-to-chlorine generators should be maintained at 60-80 ppm because the generated chlorine has no stabilizer built in.  At levels over 60 ppm it tends to cause false readings on Total Alkalinity tests.  Our Water Lab automatically adjusts for that.  There is a theory that very high levels (over 120 ppm) can cause chlorine lock where the chlorine stops working. 

     While there is no good scientific data on exactly where Chlorine Lock starts (it’s probably more of a range than a place), you may be advised to partially drain the pools, in order to dilute levels over 100 ppm.  Over-stabilizing is generally not a problem unless you use too much chlorine, or you stabilize water that didn’t need it. 

3.  Acid Demand and Base Demand are tests done just to help some computer programs calculate how to adjust your pH.  Their readings have nothing to do with anything that you would do yourself. 

4.  Phosphates.  In order to protect salt generator cells and reduce algae attacks, you should keep phosphates below 1000 ppb.  Currently, we agree with that number for salt-to-chlorine generators, but we think that doesn’t make economic sense for algae prevention.  So don’t buy a phosphate remover unless: 

A. You have a salt-to-chlorine generator and you’re over 1000 ppb

B.  or You are having multiple algae attacks or you are using too much chlorine

C.  or Your level is over 2500 ppb

D.  or You just want to be positive that nothing goes wrong. 

     All those phosphates don’t hurt you, but they grow algae in pools, ponds and lakes.  They also ruin the salt-to-chlorine generator cell so that you have to run it much longer to keep up.  And that causes you to spend more money on chemicals just to stay ahead of it.  If you have a salt-to-chlorine generator, don’t use cheap salt that has YPS as an anti-caking agent.  That’s a phosphate.  Avoid the cheaper stain, scale, mineral or metal control chemicals.  They are also phosphates.

                                                                                      Please let us help you, anytime.                                                Revised:  8/14/12


Pool Size: ___________ Gallons Technician: ___________
Date: ________________

We write Pool Tips for the exclusive use of our own local customers. They are meant as a summary of general information, to be discussed in our store, with our staff, to determine which items are best for specific pools. Pool Tips are a trademark of Gull Group, Inc. All rights reserved.

Our suggestions assume that you have given us a proper description of your pool’s size, history and symptoms. Sometimes we can figure it out, sometimes we can’t. Your doctor has years more training, far better diagnostic tools, and makes way more money—and sometimes he or she gets it wrong, too.

  1. Read all labels carefully, and only use chemicals exactly as described on the label. Never mix chemicals together outside of the pool. Some of them can cause a fire or explosion.
  2. Do Not follow any advice or suggestions here without coming into the store, customizing them to your specifics, and receiving them in writing.
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  4. Don’t Blame Us for anything. It’s free advice, and worth the price paid. We’re trying to help, but pools are complex, and chemicals and electricity are dangerous.
  5. Our Best Advice: Go find a local pool dealer who knows what they are doing, become a steady customer, and give them a chance to learn about you and your pool. Pick a brand, pick a store, and stay with them.